This invention relates to a system for indicating the presence of moisture in absorbent pads, such as disposable diapers, surgical dressings, sanitary napkins, etc., and to garments such as diapers and other absorbent materials incorporating the moisture indicating system. An enzymatic system used in conjunction with a chromogen visually signals the presence of moisture. The invention may further be quantitatively used to signal the presence of degrees of moisture.
In general, the prior art shows indicators which are dependent upon masking mechanisms where darker dyes are exposed when moistened, and/or non-enzymatic chemical interactions wherein color changes are dependent upon the presence or absence of acidity (e.g., litmus paper indicators), halides, which are potentially toxic, or other indicators which are complicated, uneconomical, hazardous or otherwise unsatisfactory to the wearer or user.
For example, Baker et al. U.S. Pat. No. 3,675,654 utilizes dry agents between a translucent backing and an absorbent pad, including a water soluble dye mixed with a masking agent such as talcum powder. When the pad becomes moistened, the water soluble dye becomes visible.
Likewise, Wang U.S. Pat. No. 3,759,261 adds multiple masking layers of cloth or paper over a printed pattern. When the diaper is wet, the originally opaque masking layers become translucent, revealing the printed pattern.
Similarly, Sheppard et al. U.S. Pat. No. 3,702,610 employs a water dispersible dye-containing adhesive in a spaced visible pattern to bond layers of a diaper or sanitary napkin together. When the item has been dropped in a toilet, water eventually disperses the dye-containing adhesive. When the adhesive no longer forms a discrete pattern, this informs the user of the disposable diaper or napkin that it can then be successfully flushed down the toilet. A later refinement of Sheppard was Timmons et al. U.S. Pat. No. 4,022,221, which applied the same mechanism to a different function, i.e., moisture indication to determine whether or not the diaper was in need of changing.
While all of these systems involving dyes and masking have been somewhat effective to indicate the presence of moisture, they have been unduly complicated, have required substantial quantities of materials, and as a rule have been non-discrete and non-quantitative indicators.
Other patents have disclosed systems which rely simply on chemicals which change color when wet. For example, Summers U.S. Pat. No. 3,952,746 discloses an elaborate system of transparent windows and pockets placed in a diaper, using litmus paper, food coloring, or "humidity indicator paper" to detect moisture. Summers' patent is directed more toward diaper construction than at developing a system of moisture indication.
Likewise, Eidus U.S. Pat. No. 3,731,685 proposed a moisutre indicating strip or wick as a mechanism to be attached to a garment for the purpose of detecting moisture. The patent refers to chemicals which change color when wet such as litmus paper or food coloring.
Korodi et al. U.S. Pat. No. 3,918,454 sets forth a mechanism for diaper construction involving an indicator layer impregnated with dye which becomes visible when wet. Apertures in the absorbent layer of the diaper conduct wetness to the indicator layer.
Shaw, in U.S. Pat. No. 2,681,032, uses a mechanical principle as a moisture indicator. When the diaper becomes wet, a low-wet strength element breaks, moving a colored indicator into registry with an aperture through which it is visible.